ABA2Gene Regulates Seed Development In Arabidopsis

Seeds are the most important resources for human food, and seed size is one of the mainfactors affecting crop yield. Investigations on the molecular mechanisms determining seedsize are important for understanding seed development and the improvement of crop yield.Abscisic acid (ABA) is an important plant hormone that involved in many physiologicaland developmental processes, such as storage protein synthesis, desiccation and salt tolerance.However, the molecular mechanisms of ABA in the regulation of seed size are poorlyunderstood. Here we provide important information about the mechanisms underlying theroles of ABA in the regulation of seed size in Arabidopsis through the ABA-deficient mutantaba2.Our results showed that the silique of aba2was about15.3%shorter than that of wildtype, and the seeds number per silique in aba2was13.3%less than that in wild type. Theweight per hundred seeds of aba2was118.4%of that of wild type. Furthermore, thecotyledon area of aba2was1.16-fold larger than that of wild type, but the area of aba2cotyledon cells was slightly reduced, indicating that the cell number of embryo of aba2wasincreased. Developmental processes of seed in aba2mutant were retarded compared with thatof wild type. In situ hybridization revealed that ABA2was predominately expressed inembryos at different development stages. These results suggest that ABA2was involved in thecontrol of seed development.Endogenous ABA levels in aba2silique were found to be decreased in silique of aba2mutant. Further, the application of exogenous ABA with100μM could restore the phenotypesof aba2, indicating that ABA regulated seed size through affecting the development ofArabidopsis embryo.To investigate the molecular mechanisms of ABA affecting seed size by regulating seeddevelopment, expression levels of several seed development-related genes in aba2mutantwere analyzed by qRT-PCR. The transcript levels of SHB1in silique were up-regulated at6days after pollination in aba2mutant，suggest that SHB1might be regulated by ABA2during seed development. The weight per hundred seeds of aba2shb1-L double mutant was less thanthat of aba2and resembles that of shb1-L, indicating that SHB1acted downstream of ABA2.